Since 6-1-71, the National Cancer Institute has supported a study of fast neutron beam radiation therapy of cancers in humans by the faculty and staff of the University of Washington. During the first 2 years, a medical treatment beam was developed at the University of Washington cyclotron by the staffs of the Division of Medical Radiation Physics and the cyclotron group. This beam, using 21.5 MeV deuterons to strike a beryllium target of "intermediate" thickness (70% of incident deutrons absorbed), has depth dose characteristics comparable to 60Co teletherapy and an output of about 40 rad per minute at 125 cm from the target. The collimation developed for the fixed horizontal beam allows patient application within standards of safety used in conventional photon radiation therapy. During the second 3-year grant period, the physics staff continued to refine theoretical and clinically oriented dosimetry. A computerized treatment control system was developed and made operational. Custom-made patient holding devices, i.e., chair, table and kneeling bench were developed. Prior to clinical application, the fast neutron beam was biologically characterized by the staffs of the Division of Radiation Biology and the Experimental Radiation Oncology section. Acute and long-term RBE's were determined for several tissues. OER's were determined at several sites in an absorber. Animal tumor systems were developed for use in determining therapeutic ratios and treatment patterns. Patient treatment started 9-10-73. Phase I studies of the treatment of patients with glioblastoma multiforme and extensive metastases to the neck were adequately completed for publication. Protocols were developed in cooperation with the staffs of the M.D. Anderson-TAMVEC and MANTA for: glioblastoma multiforme; epidermoid carcinomas of the oral cavity.